1. Field of the Invention
The present invention relates to an exposure technique for transferring a pattern onto a substrate such as a wafer in the lithography process for producing various devices such as a semiconductor device, a liquid crystal display device, or a thin-film magnetic head, and in particular, the present invention is preferably used for multiple exposure, for example, double exposure of a substrate.
2. Description of the Related Art
The double exposure method is one of the exposure methods used for transferring a pattern of a reticle as a mask onto a wafer (or glass plate or the like) coated with a resist to produce a semiconductor device or the like. In this method, for example, in the case that a pattern, in which a periodic pattern and an isolated pattern are present in a mixed manner, is exposed onto a same layer on a wafer, the reticle pattern is split (divided) into a first pattern corresponding to the periodic pattern and a second pattern corresponding to the isolated pattern, and these two patterns are successively double-exposed by optimizing an exposure condition, thereby obtaining high imaging performance. Conventionally, when the exposure is performed by using such a double exposure method, a first exposure is performed by using a first reticle on which at least one piece of the first pattern is formed, and then the first reticle is exchanged with a second reticle on which at least one piece of the second pattern is formed and the second exposure is performed. However, when the exposure is performed by exchanging the reticles in this manner, any high throughput cannot be obtained.
Therefore, there is proposed an exposure method in which first and second patterns are formed in advance on one reticle, the first and second patterns of the reticle are transferred onto first and second shot areas adjacent on a wafer respectively, and then the wafer is step-moved in the scanning direction by a distance corresponding to one shot area and the first and second patterns of the reticle are transferred on the second and third shot areas on the wafer, thereby double-exposing the first and second patterns onto the second shot area (see, for example, Japanese Patent Application Laid-open No. 11-111601). In this exposure method, by changing the illumination condition between the first and second patterns at the time of scanning exposure, the illumination condition can be optimized with respect to the two patterns.